Salt stress effects on growth, osmotic adjustment, mineral and organic contents and soluble peroxidase activities were determined in roots and leaves of Atriplex halimus and their corresponding callus cultures. Low NaCl doses (150 mM) promoted shoot growth, corroborating the halophilic nature of this species; in these stress conditions, Na+ concentration markedly increased in the leaves indicating that salinity resistance was not associated with the ability of the plants to restrict sodium accumulation in the aerial part. Whole organs and their corresponding calli were able to cope with high NaCl doses but there was no clear correspondence between the physiological behaviour of cell culture and whole plant. For several physiological parameters (osmotic potential (&#936;s), mineral content, proline accumulation), roots were less affected by NaCl than leaves while both root and leaf calli behaved in the same way in response to salinity. NaCl-induced modifications of the recorded parameters are discussed in relation to the mechanisms of salinity resistance in this species. Evidence indicated the existence of a cellular basis for salinity resistance in A. halimus, but the expression of this cellular property at organ level appeared to be masked by the physiological complexity of the intact plant and the nature of the whole organ response was apparently determined primarily by regulation mechanisms assigned by the differentiated tissue organization.